Fix two bugs in the extension actions toolbar

Fix two bugs in the extension actions toolbar

1. Previously, we didn't animate the browser actions
   container when the visible count changed, because we set
   the width prior to calling animate. Fix it by animating to
   the desired width.
2. There was a bug where we would improperly hide an extension
   upon loading another, because we wouldn't account for the
   chevron width. Fix this, and add a test.

BUG=410348
BUG=410361
Committed: https://crrev.com/b1a2fc8cfeb5a38360b622f030f1e756df475cfe
Cr-Commit-Position: refs/heads/master@{#293947}

[Devlin, 2014-09-03 17:26:01]

Patchset #2 (id:20001) has been deleted

[Devlin, 2014-09-03 17:26:04]

Patchset #1 (id:1) has been deleted

[Devlin, 2014-09-03 18:58:42]

rdevlin.cronin@chromium.org changed reviewers:
+ finnur@chromium.org

[Finnur, 2014-09-05 10:22:12]

Sorry, this slipped through the cracks. Only noticed it now.

LGTM.

[Devlin, 2014-09-05 15:45:23]

rdevlin.cronin@chromium.org changed reviewers:
+ sky@chromium.org

[Devlin, 2014-09-05 15:45:24]

Scott, mind taking a quick look for OWNERS?

[sky, 2014-09-05 19:12:59]

LGTM

[Devlin, 2014-09-08 21:58:55]

The CQ bit was checked by rdevlin.cronin@chromium.org

[commit-bot: I haz the power, 2014-09-08 22:03:36]

CQ is trying da patch. Follow status at

https://chromium-status.appspot.com/cq/rdevlin.cronin@chromium.org/539543002/...

[commit-bot: I haz the power, 2014-09-09 05:38:59]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-09-09 05:39:00]

Try jobs failed on following builders:
  win_chromium_x64_rel_swarming on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[Devlin, 2014-09-09 15:31:22]

The CQ bit was checked by rdevlin.cronin@chromium.org

[commit-bot: I haz the power, 2014-09-09 15:31:55]

CQ is trying da patch. Follow status at

https://chromium-status.appspot.com/cq/rdevlin.cronin@chromium.org/539543002/...

[commit-bot: I haz the power, 2014-09-09 16:09:30]

Committed patchset #2 (id:60001) as c7ecac2ad0213d039f5a03fe9676153862010ed4

[commit-bot: I haz the power, 2014-09-10 03:53:38]

Patchset 2 (id:??) landed as
https://crrev.com/b1a2fc8cfeb5a38360b622f030f1e756df475cfe
Cr-Commit-Position: refs/heads/master@{#293947}